The present invention relates to light stimulators, and more particularly relates to a novel LED variable light source constructed for use in light stimulators for retinal examinations, and the study (characterization) of light-sensitive cells and devices.
Incandescent light sources, and light emitting diodes (LEDs) are known to be used for applying pulsed light for the stimulation of light sensitive cells during retinal examinations. Currently available instrumentation for implementing retinal examinations uses a combination of lenses, filters, and shutters to direct light from a light source to achieve the retinal stimulation/examination. For example, U.S. Pat. No. 4,618,230, to Ens, et al. (“the '230 patent”), discloses a light stimulator that provides light for stimulating the retina's of a patient's eyes during a visual (retinal) examinations. Light stimulation is required to elicit data concerning retinal functioning during intracellular recordings, electroretinograms (ERGs), electro-oculograms, and other light evoked examinations.
The light stimulator disclosed by the '230 patent utilizes a pulsed light source and light directing means for directing the light generated by the pulsed light source into the patient's eyes (typically to irradiate (stimulate) the retina). The light stimulator also includes attenuator means for selectively attenuating the pulsed light source, photodetector means for capturing an output signal representative of the radiant energy directed into the patient's eyes and signal processing means for receiving and processing the output signal to derive further signals representative of the radiometric or photometric characteristics of the radiant energy. A light shutter comprising first and second shutter leaves affixed to shafts of a first and a second galvanometer is also included with the disclosed light stimulator. Attenuation control means provide for selectively varying current signals applied to the galvanometers to selectively pivot the control leaves thereby selectively varying the light used in an eye examination.
Known instrumentation that includes such known visual stimulators for carrying out electroretinograms, electro-oculograms, and other visually evoked examinations are further known to be bulky and expensive. Moreover, the '230 patent describes that its visual stimulator and incandescent light source further require R, G and B optical filters to filter the pulsed light generated in the incandescent light source to realize the proper wavelength of the light to be used for an examination, where wavelength defines color.
These restrictions yield losses in terms of the power generated by the incandescent or arc lamps and the power delivered to each target. The radiant power of incandescent or arc lamps extends from the ultraviolet (UV) to the infrared end of the spectrum, covering the visual spectrum in its entirety. Monochromatic flashes used for visual stimulation in clinical and basic research studies only require a narrow bandwidth, 10 to 20 nm wide. Thus the color filters block over 90% of the power emitted by the incandescent or arc lamps. Put in other words, 90% of the power is wasted by this means. Additional power loss results from the inefficacy of the timing mechanism.
The incandescent light is ‘on’ for the duration of the experiment or clinical examination. During a flash a mechanical shutter opens and light is delivered to the eye. However the duration of the flashes (which is a few msec in duration) is insignificant when compared to the time the incandescent or arc lamps are on. Thus, a large amount of power is wasted by this means. Incandescent and arc lamps are not designed to operate in pulsed regimes. Another option is using the new generation of ‘pulsed’ arc lamps, however their cost is several-fold higher than the LED solution we propose and also require color filter option for their operation.
In some known applications requiring light stimulators, or light stimulation, pulsed light-emitting diodes (LEDs) are used in place of more conventional incandescent light sources. Such pulsed LEDs are semiconductor devices that operate within known light stimulators to emit incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction, i.e., electroluminescence. Pulsed LEDs are available in colors that represent the entire visual spectrum, with bandwidths of about 20-30 nm. The use of pulsed LEDs in lieu of conventional incandescent lights is particularly attractive to scientists using light stimulators to study visual processes, such as those elicited during electroretinograms, electro-oculograms, and other visually evoked examinations.
Pulsed-LED devices, however, have limitations. Intensity of the flash is governed by the frequency of the pulses. Higher frequency of the pulses results in brighter flashes. Lowering the frequency of the pulses produces dim flashes. At extremely low frequencies the number of pulses is sparse and light-sensitive cells with fast responses may discriminate between pulses. A second limitation at dim levels regards the step-wise rather than continuous regulation of light intensity. One pulse is the lowest intensity possible. The next lowest light intensity would result from two-pulse application and so forth. Selection of a continuous range of intensities is particularly desirable at the low range of intensities.
LEDs are inexpensive as compared with traditional incandescent light sources, and display high power efficiency. LEDs display extremely fast on and off set times, for example, on an order of less than one millisecond. Recent advances in LED technology have realized superluminescent diodes (SLDs), which are edge-emitting semiconductors that operate based on superluminescence principles. SLDs result in a 10-fold increase in luminance (intensity of emission) over conventional LEDs. Moreover, the miniaturization of SLDs affords three or more different SLDs, e.g., R, G, B, on a single chip, or chip package. In one embodiment, an SLD is used that is manufactured by Lamina Ceramics, Westhampton, N.J.
What would be desirable in the art of controlled light sources and light stimulation applications in research and medicine is a LED variable light source comprising an SLD and light source components for controlling the SLD for particular applications requiring retinal stimulation that is more compact, more flexible and more user friendly than conventional light sources embodying a fully electronic construction that overcomes the shortcomings of the prior art.